Metal detector having target characterization and search classification

ABSTRACT

A metal detector is provided with circuitry for producing a plurality of vector signals derived from a target signal. Each of these vector signals corresponds to a phase characteristic of target signals. These vector signals define phase ranges which correspond to classifications of targets. Upon detection of a target signal, the metal detector generates first and second phase detected signals which in turn generate a plurality of vector signals. These vector signals are digitized and within a microprocessor a determination is made through slope analysis to determine which range includes the principal phase of the detected target signal. The vector signals which define the identified range are then utilized in algebraic calculations to define one of a plurality of subphase ranges within each range. This identified subphase range identifies a segment in a linear display which is illuminated to show the determined characteristic for the detected object. An operator can program the detector to select or reject target objects having certain electrical characteristics and this is likewise displayed to the operator. When the detector determines that a target signal has the same characteristics as selected by the operator, an audio output is generated. The display provided to the operator enables the operator to easily select or reject specific signal characteristics pertaining to certain types of targets.

FIELD OF THE INVENTION

The present invention pertains in general to metal detectors and inparticular to a metal detector which can permit the operator to classifythe search parameters for targets and characterize the targets whichhave been located.

BACKGROUND OF THE INVENTION

It has been well established that metal detectors can identify targetsto some degree based upon their physical composition due to the phasecharacteristics of a receive signal produced when the target object isin the field of an electromagnetic signal. Patents which illustratetarget identification based upon phase include U.S. Pat. Nos. 4,334,191to Podhrasky, 4,700,139 to Podhrasky and 4,507,612 to Payne.

Various metal detectors have been marketed which provide for targetselection by operator classification. A representative product of thistype is the Model "Eagle II" manufactured by White's Electronics ofSweethome, Oreg. In the operation of this metal detector, the operatorcan select target characteristics over a range of 1 to 100. This metaldetector assigns a response number to targets based upon theirelectrical characteristics. The operator can program the detector tohave selected search numbers which correspond to certain physicalcharacteristics of desired targets. When the White's "Eagle II" detectsan object and classifies it with the same number as has been previouslyselected by the operator, an audio output is produced along with avisual display indicating a match between the operator's programmedselection and the classification of a particular target. The display andoperation, however, are principally numerical, with limited wordindicators for target type, and the operator must relate particularnumbers in the 1 to 100 range for correlation to desired targets.

In view of the desirability of easily classifying targets desired fordetection and for indicating the nature of detected targets, there exista need for a method of operation and a display for a metal detectorwhich makes operation easy and simple for the operator for and providesaccurate target classification and response.

SUMMARY OF THE INVENTION

A selected embodiment of the present invention is a targetcharacterization display for a metal detector in which there is produceda detection signal for objects that are present in the region of thedetector. The display includes a first set of display segments and anarray wherein each of the segments has a first and second display state.A discrimination memory is provided which has respective storagelocations for each of the segments of the display. Each of thediscrimination memory storage locations corresponds to a unique signalparameter range for targets of the metal detector. The value stored ineach of the discrimination memory storage locations corresponds to thedisplay state for the corresponding display segment. There is furtherincluded a second set of display segments arranged in an array whereineach of the segments has a first and second display state. The secondset of display segments are positioned in proximity to the first set ofdisplay segments and there is a correspondence between the segments ofthe first and second sets. A target memory is provided which hasrespective storage locations therein for each of the display segments inthe second set of segments. The values in the target memory storagelocations are derived from the detection signal produced by the metaldetector for the target object. The values stored in each of the targetmemory storage locations corresponds to the display state for thecorresponding display segment.

In a further aspect of the present invention, there is provided a methodof operation for a signal processing circuit used in conjunction with ametal detector circuit which produces multiple detection signals thatrepresent a target vector signal related to target object composition.This method includes the steps of producing first and second vectorsignals which are related to the target composition. Next, there areproduced a plurality of signals which are algebraic combinations of thefirst and second vector signals. Each of the vector signals is examinedto determine a pair of the vector signals which encompass the phaserange of the target vector signal. The pair of vector signals arealgebraically combined to produce a target identification value. Afterproduction of the target identification value, a determination is madeto find a subphase range into which the vector signals for the target ispresent. This indicates a physical characteristic for the target object.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a metal detector which incorporates thefeatures of the present invention,

FIG. 2 is a block diagram of the electronic circuitry of the metaldetector of the present invention,

FIG. 3 is a schematic circuit illustration of the multiple phase vectorgenerator circuit shown in FIG. 2,

FIG. 4 is a diagram illustration of the vector signals produced by thephase vector signals produced by the phase vector generator circuitshown in FIG. 3,

FIG. 5 is an illustration of a liquid crystal display screen and atouchpad for the present invention,

FIG. 6 is a flow diagram illustrating the steps of initializing theoperation of the metal detector of the present invention to set targetdiscrimination,

FIG. 7 is a block diagram for the operational aspects of invention asapplied to the microprocessor 56 for determining the targetidentification value, that is subphase range, for a target signal,

FIG. 8 is a detailed flow diagram representing the processes carried outin operational block 232 introduced in FIG. 7 for identifying thepresence of a target,

FIG. 9 is a detailed flow diagram representing the operations carriedout in block 234, shown in FIG. 7, for determining into which the targetsignal is classified, and

FIG. 10 is a detailed flow diagram illustrating the steps which arecarried out in the operational block 23 of FIG. 7 for determining targetidentification values which in turn determines which segment of thetarget segments of the display are illuminated.

DETAILED DESCRIPTION

The present invention is a circuit and display for a metal detector,such as a hobby-style metal detector 20 as shown in FIG. 1. The detector20 includes a first stem section 22, second stem section 24 and aninterconnecting hand grip 26. A housing 28 includes electronic detectioncircuitry, described below, together with a display and an operatortouchpad, also described below. The metal detector 20 is provided, witha search coil 32 which is connected via a cable 30 to the electronicswithin the housing 28. The detector 20 is further provided with an armrest 34 which is mounted on the stem section 24. A battery and speakerhousing 36 is connected to the stem 24 and arm rest 34. A cable, notshown, extends from the housing 36 through the stem 24 and grip 26 tothe housing 28 for connection to the electronic circuitry therein.Batteries within the housing 36 provide electrical power for thecircuitry, described below. A speaker within the housing 36 provides anaudio signal to the operator which is generated by the circuitry withinthe housing 28.

The present invention is an easily usable metal detector which includessimple programming to select desired targets, a unique display toindicate the targets which have been programmed, as well as a displayfor classification of targets which have been found. The inventionfurther includes a method of processing signals produced by a targetobject to provide target classification.

The operation of the electronics of the present invention is shown in ageneral block diagram in FIG. 2. A detector circuit 50 functions in aconventional manner of a balanced induction metal detector to producefirst and second phase detected signals. Such a circuit is described inU.S. Pat. No. 4,700,139, filed Oct. 29, 1984, to Podhrasky which isassigned to the assignee of the present application. U.S. Pat. No.4,700,139, filed Oct. 29, 1984, is herein incorporated by reference.

The output from the detector circuit 50, which corresponds to the signallines 36 and 38 of U.S. Pat. No. 4,700,139 in FIG. 1 thereof, are inputto a multiple phase vector generator circuit 52. This circuit isdescribed in detail in FIG. 3. Circuit 52 produces multiple targetvector signals which represent vector components of the detected targetsignal.

The target vector signals produced by the circuit 52 are provided to ananalog-to-digital converter 54 which digitizes the received signals andprovides them to a microprocessor 56. A representative microprocessorwhich functions in accordance with the present invention is a ModelMC68HC705 manufactured by Motorola.

The microprocessor 56 receives operator inputs from a touchpad 62, whichis further described, in reference to FIG. 5. A liquid crystal display60 is driven by the microprocessor 56. This display is further shown inFIG. 5. The microprocessor 56, upon detection of a target signal havingcertain electrical characteristics and matching a previousdiscrimination selection, produces a signal that is transmitted to anaudio circuit 58 to produce an audio output to an operator. Such anaudio circuit is shown in U.S. Pat. No. 4,700,139.

Briefly, in operation, the metal detector 20 is operated such that thesearch coil is moved over the surface of the ground in the region of atarget. The target distorts the electromagnetic field produced by thetransmit coil and thereby induces a signal in the received coil. Thisreceived signal is phase demodulated to produce two phase detectedsignals which are provided by detector circuit 50 to the multiple phasevector generator circuit 52. The circuit 52 utilizes these two phasedetected signals to produce a plurality of vector signals representingphase components of the original target signal. These are produced byvarious summations and amplifications of the input signals The vectorsignals are then input to the analog-to-digital converter 54 fordigitization and the resulting digital samples are provided to amicroprocessor 56 for evaluation in accordance with selected processingsteps which are further described below in detailed flow diagrams.

An operator determines the nature of a desired target and inputs thisinformation through a touchpad 62 while observing the output from theliquid crystal display 60. The microprocessor 56 stores the selectioninformation and displays it to the operator through the liquid crystaldisplay 60. The operator initiates the searching procedure by inputtinga command through the touchpad 62. When the microprocessor determinesthat a target signal has been produced which has the characteristicspreviously selected by the operator, this will be indicated both on theliquid crystal display, 60 and by means of an audio tone which isgenerated through the audio circuit 58. A further detailed descriptionof the metal detector in accordance with the present invention isprovided in reference to the descriptions of the following Figures.

The multiple phase vector generator circuit 52, introduced in FIG. 2, isdescribed in detail in FIG. 3. Signals at lines 66 and 68 are first andsecond phase detected signals which are produced as described inreference to U.S. Pat. No. 4,700,139 at lines 36 and 38 shown in FIG. 1thereof. The phase detected signal at line 66 is provided to adifferentiation circuit 70 which produces a second derivative of theinput signal and provides this second derivative signal at an outputline 71. The phase detected signal at line 68 is provided to adifferentiation circuit 72 which likewise provides a second derivativesignal at an output line 73. The signal at line 71 is designated as S1Lwhich stands for signal 1, low amplitude. The signal at line 71 is inputto a low pass filter and amplifier 74 which produces a signal termed S1Hwhich is a low pass filtered and amplified signal derived from thesignal S1L.

The signal at line 73 is designated as S4L. The S1L signal istransmitted through a resistor 76 and the S4L signal is transmittedthrough a resistor 78 to a line 79 to produce a signal S2L. The S2Lsignal is transmitted through a low pass filter and amplifier 80 toproduce a signal S2H.

The S1L and S4L signals are likewise transmitted through respectiveresistors 82 and 84 to a line 85 to produce a summation signal which istransmitted through a low pass filter and amplifier 86 which produces asignal S3H.

The S1L signal at line 71 is transmitted through an inverter 90 and aresistor 88 to a line 89. The S4L signal is provided through and aresistor 92 to the line 89 for summation with the S1L signal. Theresulting summation signal at line 89 is transmitted through a low passfilter and amplifier 94 to produce a signal S5H.

The S1L signal at line 71 is also transmitted through an inverter 98 anda resistor 96 to a line 97. The S4L signal at line 73 is transmittedthrough a resistor 100 for combination with the S1L signal at line 97 toproduce a signal S6L. The S6L signal at line 97 is provided to a lowpass filter and amplifier 102 for production of a signal S6H.

As described above, the "H" signals are amplified and filtered versionsof the corresponding "L" signals. The signals S1L, S1H, S2L, S2H, S3H,S4L, S4H, S5H, S6L and S6H are target vector signals which representselected phase components for target signals Without the "H" and "L"designations, the signals are S1, S2, S3, S4, S5 and S6.

Further referring to FIG. 4, there is illustrated a phase diagram whichrepresents target vector signals produced by the circuit 52 and adefinition of targets which would correspond to the vector signals. Thesignals S1H, S2H, S3H, S4H, S5H and S6H correspond respectively tovectors 120, 122, 124, 126, 128 and 130. The vectors define ranges asshown in the vector diagram. The vectors 120 and 122 define a range 121which essentially includes the responses of soil with nonconductive ironcontent as well as soil with moderate conductive components. The vectors122 and 124 define a vector range 123 which defines a range of responseswhich include targets such as bottle caps. The vectors 124 and 126define a range 125 which includes targets such as nickels. The vectors126 and 128 define a range 127 which includes targets such as pull-tabs.The vectors 128 and 130 define a vector range 129 which includes targetssuch as rings. Finally, the vector 130 and line 132 define a phase range131 which includes targets such as highly conductive coins. These phaseranges are related to display segments which are shown in FIG. 5.

Referring to FIG. 3, the resistor values are as follows:

Resistor 76=22K ohms

Resistor 78=270K ohms

Resistor 82=22K ohms

Resistor 84=4.9K ohms

Resistor 88=68K ohms

Resistor 92=47K ohms

Resistor 96=47K ohms

Resistor 100=47K ohms

A further significant aspect of the present invention is a display 150which is illustrated in FIG. 5. The display includes a linear array 152of target indication segments, one of which is segment 160 It furtherincludes a linear array 154 of discrimination segments, one of which issegment 162. The segments in arrays 152 and 154 are preferably liquidcrystal display segments which have first and second display states,namely light and dark corresponding to reflective and nonreflectivestates.

The signals S1, S2, S3, S4, S5 and S6 are marked on FIG. 5 together withthe ranges 121, 123, 125, and 127, 129 and 131. These target vectorsignals and ranges correspond to sections of the display for the arrays152 and 154. The target array 152 segments are illuminated by themicroprocessor 56 when a target signal is classified in one of thecategories corresponding to one of the twenty-four segments.

The array 154 segments are selected by an operator to define particulartargets for which the operator wishes to either receive an audiblenotification when they are detected or wishes to specifically reject.

The metal detector 20 has various modes of operations which areindicated on the display 150 by the operational indicators "COIN DEPTH","PINPOINT SELECT" and "OPERATE".

The display 150 further includes various operational modes andprogramming features which are indicated by words.

The operator provides inputs to the microprocessor 56 by operation of atouchpad 62. The touchpad 62 includes a power key 164, a negativeincrement key 166, an accept key 168, a reject key 170, a last mode key172, a pinpoint key 174, a select key 176, an operate key 178 and apositive increment key 180. Operation of the subject metal detector inconjunction with the display 150 is further described below.

Referring now to FIG. 6, there is illustrated a flow diagram fordiscrimination selection setup of the metal detector 20 in accordancewith the present invention. Target discrimination can be implemented foreither accepting specifically defined targets or rejecting specificallydefined targets. This further can be done by either first or secondmethods as described herein. Basically, the operator can (1) accept orreject a specifically defined signal target type or (2) physicallydetect the target through operation of the metal detector 20 andfollowing classification of the target select whether that type oftarget is to be accepted or rejected.

Further referring to FIG. 6, entry is made to an operational block 200for implementing method one or an operational block 210 for implementingmethod two. In method one, operation is transferred to an operationalblock 202 in which the operator utilizes the metal detector 20 in theoperate mode to actually detect a target object. When this is done, themicroprocessor 56 displays an activated segment within the segments ofarray 152 to indicate the classification of the target. This could be,for example, segment 160. This would indicate detection of an objectsuch as foil or a bottle cap. Continuing to an operational block 204,the operator can then depress either the +key 180 to set adiscrimination register, a register corresponding to the display segment154, to accept the target or can enter operational block 206 and depressthe-key 166 to set the discrimination register for rejecting thatparticular type of target. Continuing to an operational block 208, theappropriate ones of the discriminator segments 154 are illuminated toindicate that the discrimination register has been set to either acceptor reject targets that have a corresponding classification. Followingthe completion of method one, the operation transfers from block 208 toan exit to await a further operator selection. This discriminationregister is either a register in the microprocessor 56 or a logicalregister in the microprocessor software.

Further referring to FIG. 6, if method two is selected fordiscrimination programming, entry is made to the operational block 210and further to an operational block 212. Within the block 212, thepositive increment key 180 is depressed to move an illuminated segmentof the array 154 to the right as indicated by the corresponding arrowfor the key 180. For each illuminated segment of array 154, such assegment 162, the operator can determine whether to accept or reject thatparticular type of target. Continuing to an operational block 214, theoperator has the option of moving the key 166 to the left for makingtarget discrimination selection. Following the operational block 214,the procedure continues through the previously described operationalblocks 204, 206 and 208 for the operator to press either of keys 168 or170 to set the discrimination register to either accept or reject thedetermined type of target. Further, after such a selection is made, thediscrimination segments of array 154 are appropriately set andilluminated.

Thus, in FIG. 6, the metal detector 20 is set up by the operator toselectively accept or reject target signals which have been classified,as further described below. The display 150 indicates in array 154 whichsegments (target types) have been selected. This is discriminationselection.

The functional operation of the microprocessor 56 for evaluating signalsprovided by the circuit 52 and producing the segment illumination forsegments of array 152 and array 154, as well as for the control signalfor the audio circuit 58 is shown in the flow diagram illustrated inFIG. 7. Operation is begun with an operational block 230 in which thedetector 20 receives the digital signals from the analog-to-digitalconverter 54 and stores the last N values of detection information. Forthe present embodiment, this comprises the last four samples of each ofthe ten vector signals which have been received for the target signal.The group of ten signals are sampled every five milliseconds. Thus, theprocessing is carried out after the target signals have been collected.However, this is done in a very fast processing technique such that theresponse to the operator occurs within a very short human response time.

Continuing to a decision block 232, an inquiry is made to determine if atarget is present within the received signal. This operation isdescribed in more detail in reference to FIG. 8. If no target isdetected, the exit is taken from the block 232 to return control to theblock 230. Thus, the microprocessor metal detector 20 cycles between theblocks 230 and 232 receiving and processing the information to detectthe existence of a target when in the operating mode. If a target isdetected, as determined by the decision block 232, exit is taken throughthe target exit to an operational block 234.

Within the operational block 234, a determination is made for the targetID range for the received target signal. This is a classification of thetarget signal to be within one of the ranges 121, 123, 125, 127, 129 and131 as described above and shown in FIGS. 4 and 5. A detailed flowdiagram illustrating this operation and the method of determining theparticular target ID range is shown in FIG. 9.

After the target ID range has been determined, control is transferred toan operational block 236 in which arithmetic calculations are carriedout to determine the target ID value within the previously determinedrange. This is done using the two vectors which define the selectedrange. The operations carried out in operational block 236 are describedin detail in reference to a detailed flow diagram in FIG. 10. The resultof the processing carried out in operational block 236 is anidentification of a target ID value which is a value that corresponds toone of the twenty-four segments within the target segments of array 152.Note that each of the ranges is subdivided into categories which aretermed "target ID values". Each of these values corresponds to a segmentof the display array 152 and also to a segment of the display array 154.

After the target signal has been classified down to the level of atarget ID value, control is transferred to an operational block 238 inwhich the microprocessor 56 sets a bit in a target ID register whichcorresponds to one of the segments of array 152. Each of the segmentswithin the segments of array 152 corresponds to a particular target IDvalue. A target ID register is provided which has a memory storagelocation for each of the segments of array 152. Each of the memorylocations corresponds to a range of target ID values, that is, aparticular narrow range of phase characteristics for the target signal.When the target has been identified to have a particular target IDvalue, the microprocessor 56 sets a display bit in the correspondinglocation of the target ID register to cause the corresponding one of thesegments in target array 152 to be illuminated. After this is done,operation is carried out in block 240 to display the target ID registeron the upper scale of display 150. The upper scale comprises thesegments of target array 152. Thus, the one of these segments, whichcorresponds to the physical characteristics of the target, isilluminated.

The target ID register can be either a register in the microprocessor 56as a logical register handled by the software in operation by themicroprocessor.

Following the operational block 240, entry is made to a decision block242 in which the contents of the target ID register are compared withthe contents of the discrimination register. The discrimination registerfunctions to activate the segments of discrimination array 154. Thediscrimination register has a memory storage location corresponding toeach of the segments of array 154. Note, as described above, each of thesegments within the segments of array 154 corresponds to a particularphysical characteristic of a target and likewise the segments in array154 correspond on a one-to-one basis to the segments of array 152. Thus,within operational block 242 a comparison is made to determine which ofthe corresponding memory locations have similar values (bits) toindicate that a target has been found with a particular target ID valueand the operator has previously set a similar discrimination value intothe discrimination register. If there is a comparison, the accept exitis taken to an audio response block 244 in which the microprocessor 56generates a control signal to the audio circuit 58 to produce an audiosignal to the operator to indicate that a desired target object has beendetected.

If the decision block 242 determines that there are no comparisonsbetween the target ID register and the discrimination register,therefore no target object has been found which corresponds to what wasset in the discrimination register, the reject exit is taken to anoperational block 246 and the microprocessor 56 does not send any typeof audio control signal to the audio circuit 58. However, note that thetarget segments of array 152 are illuminated showing the type of targetfound so that the operator visually knows that a target has been foundand that it has a particular physical characteristic. The outputs fromthe blocks 244 and 246 transfer control of the microprocessor 56 back tothe operational block 232 to again store received values and monitor forthe detection of a target. Further details of the operations describedin reference to FIG. 7 are presented in FIGS. 8, 9 and 10.

Referring now to FIG. 8, there is shown a more detailed explanation ofthe operation which occurs within operational block 232 in FIG. 7. Thefunction of this block is to identify the presence of a target signalwithin the received signal. This is done by examining the slope of thevector signals S1 and S2. In a decision block 250, an inquiry is made todetermine if the difference between the signal component S1H(N) andS1H(N-3) is greater than zero. This indicates that the S1 signal has apositive slope. If this difference is not greater than zero, the no exitis taken and return is made to the operational block 230 to againreceive values for the received signal. If the answer to the inquiry inoperational block 250 is positive, the yes exit is taken to a decisionblock 252 in which an inquiry is made to determine if S2H(N)-S2H(N-3) isgreater than zero This inquiry determines if the slope is positive forthe S2 signal. If the response to this inquiry is negative, the no exitis taken and return is made to the operational block 230. But, if theresponse to the inquiry is positive, the yes exit is taken and entry ismade to the operational block 234 for processing of the target signal.The operations described in reference to FIG. 8 determine that there arepositive slopes for the signals S1 and S2 at a particular time therebyindicating that a valid, nonground, target signal is present forprocessing.

Referring to FIG. 9, there is illustrated a detail flow diagramrepresenting the operations carried out in operational block 234 shownin FIG. 7. The function of the block 234 is to determine the rangewithin which the target signal is present. The possible ranges are 121,123, 125, 127, 129 or 131 as described in reference to FIGS. 3 and 4.Referring now to FIG. 9, from operational block 232, entry is made to adecision block 270 to determine if the difference between the S3 signalat two sample times is positive or negative. This is a determination ofslope between the sample points N and N-3. If the response is negative,the no exit is taken and entry is made to an operational 272 in whichthe bottle cap range, range 123, is selected. Following block 272,return is made to the operational block 236 for the arithmeticdetermination of the target ID value, which corresponds to one of thesegments 152.

If the determination in decision block 270 is positive, the yes exit istaken to a decision block 274. Within block 274, the determinationS4H(N)-S4H(N-3) greater than zero is made. This likewise is a comparisonof the amplitude of the signal S4H at two different times separated bythree samples. The approximate sample rate for the analog-to-digitalconverter 54 for use in the present invention is at five millisecondintervals. If the response in decision block 274 is negative, the noexit is taken and entry is made to operational block 276 in which thenickel range, which is range 125, is set. Control is then transferredfrom operational block 276 to the block 236.

If the response to the inquiry in operational block 274 is positive,that is the slope of the S4 signal is positive, the yes exit is taken toa decision block 278 in which the inquiry is made for S5H(N)-S5H(N-3)greater than zero. If this inquiry is negative, the no exit is taken andentry is made to an operational block 280 in which range 127 is set forthe type of targets corresponding to pull-tabs. Following block 280,return is made to operational block 236.

If the response to decision block 278 is positive, then the yes exit istaken to a decision block 282 in which the inquiry is made forS6H(N)-S6H(N-3) greater than zero. If this inquiry is negative, the noexit is taken to an operational block 284 in which range 129 is set.This corresponds to objects such as rings.

Following operational block 284, return is made to operational block 236for further signal evaluation.

If the response in decision block 282 is positive, the yes exit is takento an operational block 286 in which range 131 is set. This rangecorresponds to objects such as coins. Following block 286, control istransferred to operational block 236.

In summary, the operations carried out in this reference to FIG. 9comprise determining which of the ranges the target signal is in asshown in FIG. 4.

Referring now to FIG. 10, there is shown in detail the operations whichare specified for operational block 236 shown in FIG. 7. The overallfunction of block 236 is to determine a particular target ID valuewithin a determined range for the target signal. As described above, therange is determined in operational block 234. The functions carried outin operational block 236 comprise determining a subphase range for thetarget signal within the determined range. Each of the subphase rangescorresponds to one of the display segments 160 of target array display152. There are no display segments for range 121, which is a soilresponse. Range 123 has five segments, each of which corresponds to aparticular subphase range of the range 123. Range 125 has three segmentsand corresponding three subphase ranges. Range 127 has three segments,range 129 has five segments and range 131 has eight segments.

Operational block 234 determines the range in which a target signal ispresent and operational block 236 determines which of the subphaseranges the target signal is present for selecting one of the segments152.

Further referring to FIG. 10, entry is made to a first operational block300 for determining if the bottle cap range has been previouslydetermined. If so, the yes exit is taken to an operational block 302 inwhich signal processing is performed using the S2 and S3 signals atoffset time points. This mathematical function is shown in operationalblock 302. The result of this processing is a target value, a number.Following operational block 302, control is transferred to anoperational block 304 in which the target value is applied to a look-uptable to determine the corresponding target ID bit, that is the subphaserange within the range 123. As noted above, there are four subphaseranges. Therefore, all the possible target values have to fall into oneof these four possible sub-ranges.

If the response at the block 300 is negative, the no exit is taken to anoperational block 306 to determine if the range 125 has been previouslydetermined in block 234. If so, exit is made to an operational block 308to carry out a target value computation as shown within this block. Thisproduces a number for a target value. The range for block 308 is 125which has three segments of the array 152. This number is then used inthe next sequential operational block 310 where it is applied to alook-up table for determination of a target ID bit. There are threepossible bits which can be selected, which correspond to the segments152 for the range 125. The result of the operation in block 310 isidentification of one of these three bits. Following block 310 controlis returned to operational block 238.

If the response in block 306 is negative, control is transferred to anoperational block 312 in which it is determined if the range 127 forpull-tabs has been previously selected. If so, control is transferred toan operational block 314 in which an algebraic operation is carried outwith the S4 and S5 signals to produce a number for a target value.Following operational 314, control is transferred to an operationalblock 316 in which the target value is applied to a look-up table todetermine the corresponding target ID bit. There are three possible bitlocations for range 127 as corresponding to the segments 152 illustratedin FIG. 5. Upon selection of one of these three bits, control istransferred from operational block 316 to the operational block 238.

If the operational block 312 has a negative response, the no exit istaken to an operational block 318 in which determination is made if therange 129 has been selected in block 234. If so, control is transferredto an operational block 320 in which an algebraic operation is conductedto determine a target value utilizing the signals S5 and S6 whichexisted at times N and N-3. Following calculation of the target value inblock 320, control is transferred to an operational block 322 in whichthe determined target value is applied to a look-up table for selectinga target ID bit, corresponding to one of the possible five segments 152in the display 150. Once a selection is made for this target ID bit,control is transferred to operational block 238.

If the block 318 determines that the range 129 has not been selected,control is transferred to an operational block 324 to determine if thecoin range 131 has been selected. If so, control is transferred to anoperational block 326 in which an algebraic operation is conducted todetermine the target value based upon the signals S1 and S6. Followingthe operational block 326, this numeric target value is applied inoperational block 328 to a look-up table for determining the target IDbit. There are eight bits possible for range 131, each of these bitscorresponding to the segments of array 152 within the range 131.Following the selection of the target ID bit in operational block 328,control is then transferred to the operational block 238.

All of the sub-ranges are essentially uniformly distributed across theindividual ranges.

In summary, the present invention is a metal detector in which there isprovided a display and touchpad such that the operator can select toeither accept or reject particular target signals associated withcertain types of targets. This is the operator's discrimination functionand the results of the selection is displayed in a linear array ofsegments, each of which may have a reflective or nonreflective state. Inoperation, the circuitry of the metal detector processes the receivedsignal to produce multiple target vector signals These signals define aplurality of phase ranges and the target signal is classified within oneof these ranges. Further algebraic operations upon the pair of signalswhich define the phase range are carried out to select a discretesubphase range that more precisely defines a characteristic of thesignal, which corresponds to a physical characteristic of the targetobject This is determined by producing a target ID value. Once thisvalue is determined, a segment of the display 152 is illuminated toindicate the nature of the object which has been detected. If theilluminated segment corresponds to a previously selected segment in thediscrimination, array 154, there is produced an audio output to theoperator indicating that the target selected by discrimination had beenfound.

Although one embodiment of the invention has been illustrated in theaccompanying drawings and described in the foregoing detaileddescription, it will be understood that the invention is not limited tothe embodiment disclosed, but is capable of numerous rearrangements,modifications and substitutes of parts and elements without departingfrom the scope of the invention.

What is claimed is:
 1. A target characterization display for a metaldetector which produces a detection signal for objects in a region ofthe detector, comprising:a first set of arrayed display segments eachhaving first and second display states, a discrimination memory havingrespective storage locations therein corresponding to each of saiddisplay segments in said first set, each discrimination memory storagelocation corresponding to a unique signal parameter for metal detectortargets and wherein the value stored in each of said discriminationmemory storage locations controls the display state for thecorresponding display segment, a second set of arrayed display segmentseach having first and second display states, said second set of displaysegments positioned proximate said first set of display segments andhaving a correspondence between the segments of said first set and saidsecond set, and a target memory having respective storage locationstherein for each of said display segments in said second set, whereinthe values in said target memory storage locations are derived fromphase detected signals and wherein the value in each of said targetmemory storage locations controls the display state for thecorresponding display segment.
 2. A target characterization display fora metal detector as recited in claim, further including:means fordetecting when corresponding ones of said storage locations in saiddiscrimination and target memories have been set to values for drivingthe corresponding display segments to an active display state, and forgenerating a control signal upon said detecting, and an audio outputcircuit connected to receive said control signal and for producing anaudio output upon receipt of said control signal.
 3. A targetcharacterization display for a metal detector which produces a detectionsignal for objects in a region of the detector, comprising:a first setof linearly arrayed display segments each having first and seconddisplay states, a discrimination memory having respective storagelocations therein corresponding to each of said display segments in saidfirst set, each discrimination memory storage location corresponding toa unique signal parameter for metal detector targets and wherein thevalue stored in each of said discrimination memory storage locationscontrols the display state for the corresponding display segment, asecond set of linearly arrayed display segments each having first andsecond display states, said second set of display segments positionedessentially in parallel with said first set of display segments andhaving a one-to-one correspondence between the segments of said firstset and said second set, and a target memory having respective storagelocations therein for each of said display segments in said second set,wherein the values in said target memory storage locations are derivedfrom phase detected signals and wherein the value in each of said targetmemory storage locations controls the display state for thecorresponding display segment.
 4. A target characterization display fora metal detector as recited in claim 3, further including:means fordetecting when corresponding ones of said storage locations in saiddiscrimination and target memories have been set to values for drivingthe corresponding display segments to an active display state, and forgenerating a control signal upon said detecting, and an audio outputcircuit connected to receive said control signal and for producing anaudio output upon receipt of said control signal.
 5. A targetcharacterization display for a metal detector which has transmit andreceive coils for producing a detection signal and phase detectioncircuits for producing phase detected target signals from said detectionsignal, comprising:a first set of linearly arrayed display segments,each having first and second display states, a discrimination memoryhaving respective storage locations therein corresponding to each ofsaid display segments in said first set, each discrimination memorystorage location corresponding to a unique signal parameter for metaldetector targets and wherein the value stored in each of saiddiscrimination memory storage locations controls the display state forthe corresponding display segment, a second set of linearly arrayeddisplay segments each having first and second display states, saidsecond set of display segments positioned essentially in parallel withsaid first set of display segments and having a one-to-onecorrespondence between the segments of said first set and said secondset, and a target memory having respective storage locations therein foreach of said display segments in said second set, wherein the values insaid target memory storage locations are derived from said phasedetected signals and wherein the value in each of said target memorystorage locations controls the display state for the correspondingdisplay segment.
 6. A target characterization display for a metaldetector as recited in claim 5, further including:means for detectingwhen corresponding ones of said storage locations in said discriminationand target memories have been set to values for driving thecorresponding display segments to an active display state, and forgenerating a control signal upon said detecting, and an audio outputcircuit connected to receive said control signal and for producing anaudio output upon receipt of said control signal.
 7. A method ofoperation for a signal processing circuit used in conjunction with ametal detector circuit which produces multiple detection signals thatrepresent a target vector signal related to target object composition,the method comprising the steps of:producing first and second vectorsignals which are related to target composition, producing a pluralityof vector signals which are algebraic combinations of said first andsecond vector signals, examining each of said vector signals todetermine a pair of said vector signals which encompasses the targetvector signal, algebraically combining the pair of vector signals toproduce a target identification value, and determining within which oneof a plurality of predefined subphase ranges, which are between saidpair of vector signals, said target identification value is present,thereby indicating a characteristic of the target object.